1.3 Periodic Trends
Transcript of 1.3 Periodic Trends
2016 Trends and nuclear charge.notebook
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February 17, 2016
TRENDS IN THE PERIODIC TABLE 1.3 Periodic Trends 1) Metallic Character
2) Atomic Radius 3) Ionization Energy 4) Electron Affinity
METALLIC CHARACTER: how much an element behaves like a metal
Trend Across a PeriodMetallic Character
Trend Down a GroupMetallic Character
decreases
increases
Atomic Radiusthe distance from the center of an atom to the
outer valence shell
However, the outer shell is a cloud, so really its the distance between 2 nuclei of 2 atoms divided by 2.
3Li 4Be 5B 6C 7N 8O 9F 10Ne Across a Period:
Effective nuclear charge (Zeff ) is the “positive charge” felt by an electron. As the number of protons in the nucleus increases, so does the effective nuclear charge, which causes electrons to be attracted to the nucleus, resulting in a smaller atomic radius.
The Reason for the Trend
Across a Period: ATOMIC RADIUS DECREASES
Li C F
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3Lidown a group:
3Li
11Na
19K
37Rb
55Cs
11Na
19K
Atomic Radius increases
because there are more energy levels
atomic radius trend
IONIZATION ENERGY:the energy required to remove an electron from an atomwatch
Trend Across a period: Because there are more protons (greater effective nuclear charge) increasing the attraction between the nucleus and the valence electrons. More energy is required to overcome this attraction.
Trend Going down a group: Because electrons in the outer level are further from the nucleus (weaker effective nuclear charge), less energy is needed to remove electrons from distant energy levels.
INCREASES
DECREASES
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Question:The first I.E for Na is 495.9eVThe 2nd I.E. for Na is 4560 eVWhy is there a difference?
After Na loses its first electron it is isolectronic with the noble gas Neon. To lose a second electron would mean disrupting a stable ion; therefore the 2nd I.E is much higher.
Rearrange the following elements in order of Increasing Atomic Radius
Ne Li B
Rearrange the following elements in order of decreasing Atomic Radius
Br F Cl
Ne LiB
Br F Cl
Rearrange the following elements in order of increasing Ionization Energy
Na PAr Na P Ar
Rearrange the following elements in order of decreasing Ionization Energy
Br F Cl Br F Cl
Electron Affinity
The energy released when an electron is ADDED to a neutral atom
The electron affinities are expressed as negative values because energy is released in the formation of an ion.
As the values become more negative, the ions become more stable.
Trend: Across a Period: Electron Affinity increases (values are more negative) Why: Greater Effective Nuclear Charge increases the attraction of attractions to the nucleus
Down a Group : Electron Affinity decreasesWhy: Effective Nuclear Charge decreases because of the greater distance from the nucleus.